World number one Garbine Muguruza lost 6-2 6-0 to Caroline Wozniacki in the Pan Pacific Open semi-finals in Tokyo.
Spain's Muguruza, playing her first tournament since moving to the top of the rankings, was beaten in one hour by the Danish third seed.
"I felt my energy was a little bit low and I didn't make the important shots," Muguruza said. "I'm very disappointed."
In the other semi-final, Anastasia Pavlyuchenkova beat seventh seed Angelique Kerber 6-0 6-7 (4-7) 6-4.
Kerber lost the first eight games of the match in Tokyo and was 5-2 down in the second set.